1. Field of the Invention
This invention relates generally to unsaturated polyester resins and, in particular, to low molecular weight unsaturated polyester resins that are chain-stopped with a monofunctional alcohol or acid.
2. Description of the Prior Art
In general, unsaturated polyesters are polymers having structural units linked by ester groupings. Such polymers can be obtained by the condensation of carboxylic acids with polyhydric alcohols in accordance with the following equation: ##STR1## wherein R is the residual or remaining portion of the reactive molecule from any anhydride or dibasic acid after excluding carboxylic groups; R' is the residual from any glycol; and n is the repeating unit in the polymer chain. Most often with unsaturated polyesters, some or all of residual R is CH.dbd.CH, which is commonly derived from maleic anhydride or fumaric acid.
A typical low molecular weight unsaturated polyester can be produced by the reaction of maleic anhydride with diethylene glycol to give the following structure: ##STR2##
Alternatively, other carboxylic acids or anhydrides, such as fumaric acid, and glycols, such as propylene glycol, can be used. Typical low molecular weight unsaturated polyesters are in the form of a viscous oil having a molecular weight of about 2000 to 4000.
Low molecular weight unsaturated polyesters will crosslink in the presence of a peroxide by copolymerization with styrene or other vinyl monomers. Unsaturated maleic groups copolymerize in a 1:2 or 1:3 ratio with styrene. Several styrene molecules will react to join two ester chains together to yield an insoluble crosslinking structure.
Commercially available intermediate unsaturated polyesters usually contain about 30% styrene or other vinyl monomers. Copolymerization starts with the addition of a peroxide or other free radical catalyst and a metal dryer.
The copolymerization and crosslinking of polyesters is well known. For example, U.S. Pat. No. 3,376,273 to Masters et al relates to a process for preparing saturated polyesters which have utility in the textile field. In this process, difunctional polymer forming reactants such as dibasic acid anhydrides and monoepoxides are combined in the presence of a polyfunctional nucleus forming compound, which acts as an initiator. The initiator reacts with the monoepoxide to form a hydroxyl group or with the anhydride to form a half ester or with both.
Masters discloses the use of monofunctional chain stoppers to prevent functional groups from forming three dimensional structures. These monofunctional chain stoppers permit formation of high molecular weight thermoplastic resins from polyfunctional reactants.
U.S. Pat. No. 3,578,728 to Ehrhart et al discloses unsaturated polyester resins containing 50 mole percent of one or more dihydric alcohols and 50 mole percent of one or more dicarboxylic acids or anhydrides. Small amounts of monofunctional or polyfunctional acids or alcohols, or mixtures may be used to form the polyester resin. Larger amounts may be used if the functionality of the acid and/or alcohol mixture is maintained substantially about two.
U.S. Pat. No. 3,657,191 to Titzmann et al discloses a process for producing linear polyesters with improved stability by reacting the polyesters with ethylene carbonate or monofunctional glycidyl ether, melting the polyester and melt spinning the polyester.
Numerous processes for endcapping polyesters to improve their properties are also known. U.S. Pat. No. 4,200,731 to Massey et al relates to polyesters having molecular weights averaging from about 14,000 to 75,000, preferably from about 34,000 to 42,000. These polyesters are endcapped with benzoyl-lactams or substituted benzoylphthalimides.
U.S. Pat. No. 4,267,288 to Burkhart et al relates to hydroxy-terminated polyester urethanes endcapped with dicarboxylic acids or anhydrides to provide an acid capped polyester urethane. The acid capped chains are extended using epoxides to form epoxy-polyester-urethane block copolymers.
U.S. Pat. No. 4,379,895 to Frerking, Jr. et al discloses polyester resins having low intrinsic viscosities which are capped using an aliphatic acid, a dimer acid, an aromatic acid, or an alkyl substituted aromatic acid containing at least two carboxylic groups.
Reactive monomers which are useful for modifying polyester and vinyl ester resins are also known. U.S. Pat. No. 4,486,582 to Hefner discloses such modifiers prepared by reacting (1) an aromatic compound containing a polymerizable ethylenically unsaturated group and an group containing a hydrogen atom reactive with an NCO or NCS group, (2) a compound having at least one oxyalkylene group and at least one group containing a hydrogen atom reactive with an NCO or NCS group and (3) a compound having an average of more than one NCO and/or NCS group per molecule.
Other polyester resin compositions with desirable properties have also been prepared. For example, U.S. Pat. No. 3,457,326 to Kienle discloses a synthetic elastomer formed from (1) a linear, saturated, hydroxy terminated polyester or polyether, (2) an organic diisocyanate without isocyanate reactive groups, (3) an ethylenically unsaturated chain terminating material with less than 20 carbon atoms and containing only one group reactive with isocyanate and (4) a urea linkage forming material with at least 2 active hydrogen atoms such as diamines, water, amino-alcohols or amino phenols. The polyester used has a molecular weight between about 1000 and 4000, an acid number of less than 6 and is obtained by esterification of dicarboxylic acids and anhydrides with glycol.
U.S. Pat. No. 4,390,662 to Ando et al discloses an unsaturated polyester having improved properties. The composition includes an unsaturated polyester, which is generally hard and fragile, and an unsaturated acrylic urethane. The acrylic urethane is prepared by the addition reaction of an hydroxyl terminated polymer, a polyisocyanate and a monohydroxylalkyl monoacrylate or monohydroxylalkyl monomethacrylate.
Polyester resins have found application in a wide variety of fields. U.S. Pat. No. 4,269,798 to Ives discloses the use of polyester resins to produce artificial marble and onyx. Ives introduces a heated, catalyzed synthetic resin and filler material into the conveying section of a mixer. The conveying section forces the resin and filler through a mixing section which kneads and shears the material to uniformly disperse the resin throughout the filler. The combined resin/filler material is then introduced into a mold for curing.
U.S. Pat. No. 4,433,070 to Ross et al relates to cultured onyx products and discloses a shaped structure having a polishable cultured onyx surface, cultured marble surface or similar mineral appearing surface. The surface has a predetermined hardness with a locally discontinuous phase intimately distributed in a visually distinguishable continuous phase.
U.S. Pat. No. 4,678,819 to Sasaki et al relates to artificial marble and discloses a polymer composition in which an inorganic substance and an organic polymer are firmly bound in one body with a vinyl compound. U.S. Pat. No. 4,829,103 to Oda et al discloses an onyx like artificial marble made from an unsaturated polyester resin composition and aluminum hydroxide.
U.S. Pat. No. 3,318,727 to Boenig et al relates to the treatment of polyester surfaces with mono-, di- or polyisocyanates to provide a hardened surface with improved wear resistance that is specifically applicable to the manufacture of bowling balls. The isocyanate treated surface is then crosslinked using water or a compound with a plurality of functional groups.
U.S. Pat. No. 3,411,781 to Rytina et al discloses a cover for a bowling ball comprising a thermosetting polyester resin mix incorporating a polyfunctional crosslinking agent such as a non-polymeric esterified polyol, preferably completely esterified with a carboxylic acid. The total polyester is dissolved in styrene and crosslinked using trimethylolpropane trimethacrylate.
U.S. Pat. No. 4,253,665 to Miller, Jr. et al discloses a bowling ball having a thin film deposited on the surface from within the ball. The thin film includes a rigid unsaturated polyester resin, a flexible unsaturated resin, a saturated polyester plasticizer, and additional sufficient catalysts and promoters to cause curing of the rigid and flexible unsaturated polyester resins into a strong durable ball without binding the plasticizer to the resins.
U.S. Pat. No. 4,822,849 to Vanderlaan relates to unsaturated polyester compositions suitable as a shell for bowling balls including an unsaturated polyester prepolymer and a copolymerizable vinyl monomer cured with a polyisocyanate, a peroxide catalyst and optionally, with a peroxide activator and urethane catalyst.
U.S. Pat. No. 4,551,491 to Panush relates to a coating composition comprising a thermoplastic or thermosetting resin material containing about 1 to 20% by weight of a pigment composition.
U.S. Pat. No. 4,609,706 to Bode et al relates to high solids coatings prepared from low molecular weight unsaturated urethane containing polymers by reacting a low molecular weight hydroxylated oligomer with a bifunctional reactive monomer containing both an ethylenically unsaturated moiety and at least one isocyanate functionality. Bode et al distinguishes "alkyd resins" which include unsaturated fatty acid modified polyesters and exclude unsaturated polyesters wherein the unsaturation results largely from an unsaturated diacid or anhydride such as maleic, fumaric and the like.
U.S. Pat. No. 3,794,501 to De Nio relates to an antifouling marine paint composition including a vinyl chloride-vinyl acetate copolymer, rosin gum, pigment, polyethylene polymer, cuprous oxide, tri-n-butyltin fluoride and volatile solvents.
U.S. Pat. No. 3,898,190 to Willey relates to a marine coating composition including a binder of chlorinated hydrocarbon rubber, rosin which is at least partially soluble in sea water, an inorganic plasticizer of tricresyl phosphate, chlorinated paraffins or phthalate ester, cuprous oxide and calcium carbonate pigments and a solvent.
U.S. Pat. No. 4,021,392 to Milne et al relates to a top coat paint for ships' hulls including a film forming copolymer with at least one triorgano tin salt, a water insoluble metalliferous pigment and a hydrophobic organic retarder. U.S. Pat. No. 4,168,174 to Mixan relates to use of p-Dithiino(2,3-b)pyrazine-2,3-dicarbonitrile or 1,3-Dithiolo(4,5-b)pyrazin-2-ylidene-propanedinitrile and mixtures as antifouling agents.
In spite of the wealth of prior art, low molecular weight unsaturated polyesters with good physical properties are not readily available. It is, therefore, an object of the invention to provide low molecular weight, low viscosity unsaturated polyester resins with good physical properties.